Ignition devices

ABSTRACT

An ignition device for an internal combustion engine includes a chamber having a wall, a hole in the wall through which a medium to be ignited may communicate with the inside of the chamber, and means to produce a plasma flame within the chamber of sufficient energy to project through the hole. The means to produce the plasma flame includes first and second electrodes spaced apart by a gap. A potential from a first source is applied across the electrodes which is insufficient by itself to cause electrical breakdown of the gap, and a higher potential from a second source is applied across the gap, or a part of the gap, which is sufficient to cause the potential from the first source to be discharged across the gap.

States Patent 1191 1111 3,42,818 Cowell et a1. Oct. 22, 1974 [54]IGNITION DEVICES 2,866,447 12/1958 Kaehni 123/148 AC 2, 8,299 31959 S 131 9 [751 Inventors: Timmy Gwen; 3,250,809 1011966 182121 12311281;13911111? Cockbum Brow", both of 3,710,772 1/1973 Warner 123/169 RLeammgton Spa, England [73] Assignee: Associated Engineering Limited,Primary Examiner-Laurence M. Goodridge Warwickshire, England AssistantExaminer-Ronald Cox [22] Filed: Nov 1972 Attorney, Agent, orFtrmBr1sebo1s & Kruger An ignition device for an internal combustionengine [52] 123/169 123/143 123/191 includes a chamber having a wall, ahole in the wall 123/148 3l3/128 2 2 31 through which a medium to beignited may communicate with the inside of the chamber, and means topro- [511 '3 Cl F021 F021 23/00 Holt 13/28 duce a plasma flame withinthe chamber of sufficient [58] Field of Search 123/143 R, 143 B, 169 R,energy to project through the hole The means to 123/169 MG, 148 C, 148E, 148 AC, 148 R, duce the plasma flame includes first and second elec-313/1281 231 trodes spaced apart by a gap. A potential from a firstsource is applied across the electrodes which is insuffi- [56]References cued cient by itself to cause electrical breakdown of theUNITED STATES PATENTS gap, and a higher potential from a second sourceis ap- 1,248,828 12/1917 Dick 313/128 plied across the gap, or a part ofthe gap, which is suf- 1,253,587 1/1918 Graham 313/128 ficient to causethe potential from the first source to 1,259,240 3/1918 Jeffery 313/128be discharged across the gap, 1,272,578 7/1918 Tismer.... 123/143 B1,473,725 11/1923 Hall 123/143 B 6 Claims, 5 Drawing Figures 20 Z1 v 117 1 12 d-1 IGNITION DEVICES This invention relates to ignition devices.

The invention consists in an ignition device for an internal combustionengine including a chamber having a wall, a hole in the wall throughwhich a medium to be ignited may communicate with the inside of thechamber, and means to produce a plasma flame within the chamber ofsufficient energy to project through the hole wherein the means toproduce the plasma flame includes first and second electrodes spacedapart by a gap such that a potential from a first source applied acrossthe electrodes is insufficient to cause the breakdown of the gap and ahigher potential from a second source applied across the gap or a partof the gap is sufficient to cause the potential from the first source tobe discharged across the gap.

The discharge due to the first potential may be of substantially greaterenergy than that due to the second, higher, potential.

Means may be provided to cause the plasma flame to occur at preciselytimed intervals. The ignition device may therefore be employed inproviding ignition in reciprocating internal combustion engines.

The invention may also be employed where precise timing of the ignitionis not required.

A number of embodiments of the invention will now be described by way ofexample with reference to the accompanying drawings, of which FIG. 1 isa diagram of a first embodiment of the invention FIG. 2 is a diagram ofa second embodiment,

FIG. 3 is a diagram of a third embodiment FIG. 4 is a diagram of afurther embodiment suitable for use in an internal combustion engine,and

FIG. 5 is a circuit diagram showing the application to a multi-cylinderengine.

Referring to FIG. 1, the ignition device includes a disc-shaped frontelectrode 11 formed with a central orifice 12. The disc may be 1 inchdiameter and the orifice l/32 inch diameter, and the electrode may bel/l6 inch thick. Coaxial with the orifice 12 is a rod-shaped rearelectrode 13 which may be A inch diameter and have a smaller-diametertungsten tip 14. The bodies of the electrodes 11, 13 are of copper, orother suitable electrically-conducting material, and the rod-shapedelectrode 13 may be screwed into a rear plate 15 of copper, or otherconducting material.

An annular spacer 16 of electrically-insulating material is interposedbetween front electrode 11 and plate 15, and defines a chamber 17 whichis substantially closed, that is it is closed except for the orifice 12.A third electrode 18 projects through spacer 16 into the chamber 17, sothat its tip lies in the region between the front electrode 11 and thetip 14 of the rear electrode.

A capacitor 19 is connected across the electrodes 11, 13 and a DC.voltage V, which may be for example l00-200 volts, is applied across thecapacitor, through resistance 20. The latter may be, for example, 1,000chms. An inductor 21 is incorporated in the circuit between thecapacitor 19 and the electrode 11, which inductor may have a value of20,uI-I, and as shown the rear electrode 13 is connected to earth. Thepolarity of the electrodes 11, 13, may, however, be opposite to thatshown.

The third electrode 18 is connected to provide a precisely timedEHTpulse, and for example a conventional ignition coil and distributormay be employed to supply a pulse to the third electrode at the requiredpoint in the cycle of an internal combustion engine. The potential maybe of the order of 10 kV.

The DC. voltage V is not normally high enough to cause breakdown of thegap between electrodes 11, 13, and the EHT pulse supplied to the thirdelectrode 18 causes a spark to occur between it and the tip 14 of therear electrode 13. This causes sufficient ionisation in the chamber 17to cause the gap between the front electrode 11 and rear electrode 13 tobreak down, and the capacitor 19 discharges across the gap. The energyof this discharge is such as to cause a plasma arc to occur, the gaswithin chamber 17 rapidly heating up and expanding, causing the plasmaarc flame to project through orifice 12. The discharge continues untileither the voltage across the electrodes 11, 13 has dropped below thatrequired to sustain it, or until the rapid expansion of the gases withinchamber 17 blows out the discharge.

The embodiment of FIG. 2 is similar to that of FIG. 1, and the samereference numerals are used for similar parts. Instead of using a thirdelectrode 18, however, the EHT potential (derived for example from anignition coil and distributor system) is applied across the electrodesl1, 13, the value of the inductor 21 which is not shown in FIG. 2 butwhich couples the voltage V in a similar manner to that shown in FIG. 1being such as to avoid adverse effects on the capacitor 19, which wouldotherwise be shortcircuited. The impedance of the inductor 21 is such asto allow an RF signal across the gap between electrodes 11, 13, whichthus breaks down and allows discharge of the capacitor across the gap.

In the embodiment of FIG. 3, a third electrode 28 is positioned so thatthe current path for the EHT potential across electrodes 28, 13 is viathe front electrode 11. Thus the third electrode 28 is mounted ininsulating spacer 16 with a gap between it and the front electrode. Whenthe EI-IT pulse is applied, the gap between third electrode 28 and frontelectrode 11, and that between front electrode 11 and the tip 14 of rearelectrode 13, are in series and both break down. The ionisation of thelatter gap allows the capacitor 19 to discharge across it.

The value of the inductor 21 need not be such that its impedance islarge enough for the EHT pulse to cause a visible spark between frontelectrode 11 and rear electrode 13; too large a value of the inductortends to reduce the current in the arc resulting from the capacitordischarge, and thus reduces the energy of the plasma.

In FIG. 4, the ignition device has a front electrode 31 which iscylindrical and externally screw-threaded for insertion in the sparkplug aperture of an internal combustion engine. An orifice 32 in theelectrode 31 communicates with the combustion space of the enginecylinder (in the case of a reciprocating engine). The rear electrode 33is again rod-shaped, and is spaced from the hexagonal boss 35 of thefront electrode by an insulating spacer 36, which may be of a ceramicmaterial, e.g. alumina. Since the front electrode 31 will be effectivelyearthed in this arrangement, the polarity of the DC. voltage to beapplied to it is reversed as compared with that shown in FIGS. 1 3. Achamber 37 is formed within the electrode 31.

A third electrode 38 which is shown as a rod of similar diameter to thatof an extension of the rear electrode 33, is supported with a suitablegap from the extension by an insulating sleeve 39. An EHT pulse appliedbetween the third electrode 38 and the electrode 31 breaks down the gapbetween electrodes 38, 33 and the gap between the electrodes 33, 31, thelatter breakdown causing discharge of the capacitor 19, and thus causinga plasma arc flame in the chamber 37 and through the orifice 32 in asimilar manner to that described above.

The gap between the electrodes 11 and 28 in FIG. 2 and between theelectrodes 33 and 38 in FIG. 4 is provided so as to prevent the risingEHT voltage being passed through inductor 21 and capacitor 19 to theother electrode 14 or 31; and thereby reducing the potential differenceacross the electrodes 11-14 or 31-33. The breakdown of the gap gives asudden high frequency connection of electrode 11 to electrode 28, or ofelectrode 33 to electrode 38 which is not passed by the inductor 21.Therefore the potential difference across electrodes 11-14 or 31-33attains a high enough value to cause breakdown across these electrodes.

In place of the ignition coil and distributor, where the ignition deviceis to be employed, e.g. for starting a gas turbine engine, or forignition of a gas burner, where precise timing of the spark is notrequired, a trembler coil may be employed.

In FIG. there is shown diagrammatically a circuit for providing timedignition in a four-cylinder reciprocating internal combustion engine.This is shown as employing four ignition devices as shown in FIG. 4. Theelectrodes 31 are each connected to earth, and the electrodes 33 areeach continuously connected through inductor 21 to the high-potentialside of the capacitor 19, across which the DC. voltage V is connected.

The third electrode 38 of each device is connected through a distributor40, such as conventionally used in ignition systems, to a coil 41 forthe provision of the EHT supply.

We claim:

1. An ignition device for an internal combustion engine including a bodyofinsulating material, a first electrode, a second electrode, said bodytogether with said first and second electrodes defining a substantiallyclosed chamber, said first electrode closing one end of said chamber andbeing formed with an orifice therethrough, said second electrode beingrod-shaped and extending part-way towards said first electrode, wherebyto define a first gap between said first and second electrodes, at firstsource of electrical potential connected across said first and secondelectrodes, said potential being insufficient to cause electricalbreakdown of said first gap, and means, including a second source ofelectrical potential, at a substantially higher potential than saidfirst source, to apply said substantialy higher potential across atleast part of said first gap, whereby to ionize said part of said firstgap and thereby to cause the lower potential from the first source to bedischarged across said first gap, the energy of the discharge being suchas to cause a plasma arc to occur and rapidly heat up and expand the gaswithin said substantially closed chamber, thereby causing a plasma arcflame to project through said orifice.

2. An ignition device as claimed in claim 1, wherein said means forapplying said substantially higher potential across at least part ofsaid first gap is connected across said first and second electrodes toapply said substantially higher potential across the whole of said firstgap.

3. An ignition device as claimed in claim 1, including also a thirdelectrode, and wherein said means for applying said substantially higherpotential across at least part of said first gap is connected acrosssaid first and third electrodes.

4. An ignition device as claimed in claim 3, wherein said thirdelectrode is aligned with and spaced from said second electrode, and ison the side of said second electrode remote from said first electrode.

5. An ignition device as claimed in claim 3, wherein said thirdelectrode projects through said body of insulating material, into saidsubstantially closed chamber, between said first'electrode and saidsecond electrode.

6. An ignition device as claimed in claim 1, wherein said first sourceof electrical potential connected across said first and secondelectrodes includes capacitor means, and wherein said means for applyingsaid substantially higher potential across at least part of said firstgap includes an ignition coil and a distributor.

1. An ignition device for an internal combustion engine including a bodyof insulating material, a first electrode, a second electrode, said bodytogether with said first and second electrodes defining a substantiallyclosed chamber, said first electrode closing one end of said chamber andbeing formed with an orifice therethrough, said second electrode beingrod-shaped and extending part-way towards said first electrode, wherebyto define a first gap between said first and second electrodes, a firstsource of electrical potential connected across said first and secondelectrodes, said potential being insufficient to cause electricalbreakdown of said first gap, and means, including a second source ofelectrical potential, at a substantially higher potential than saidfirst source, to apply said substantialy higher potential across atleast part of said first gap, whereby to ionize said part of said firstgap and thereby to cause the lower potential from the first source to bedischarged across said first gap, the energy of the discharge being suchas to cause a plasma arc to occur and rapidly heat up and expand the gaswithin said substantially closed chamber, thereby causing a plasma arcflame to project through said orifice.
 2. An ignition device as claimedin claim 1, wherein said means for applying said substantially higherpotential across at least part of said first gap is connected acrosssaid first and second electrodes to apply said substantially higherpotential across the whole of said first gap.
 3. An ignition device asclaImed in claim 1, including also a third electrode, and wherein saidmeans for applying said substantially higher potential across at leastpart of said first gap is connected across said first and thirdelectrodes.
 4. An ignition device as claimed in claim 3, wherein saidthird electrode is aligned with and spaced from said second electrode,and is on the side of said second electrode remote from said firstelectrode.
 5. An ignition device as claimed in claim 3, wherein saidthird electrode projects through said body of insulating material, intosaid substantially closed chamber, between said first electrode and saidsecond electrode.
 6. An ignition device as claimed in claim 1, whereinsaid first source of electrical potential connected across said firstand second electrodes includes capacitor means, and wherein said meansfor applying said substantially higher potential across at least part ofsaid first gap includes an ignition coil and a distributor.